It is possible that just a visit from the police will be helpful. As long as everyone stays cool and respectful, everything should turn out fine. In my case, I was taken away (in handcuffs) for three days of involuntary observation, and it was at no cost to me.
This can be successful if everyone is cool and respectful. Have her practice saying, "Yes, I am suicidal and need help."
Okay, so maybe there are reasons you don't want a visit from your friendly neighborhood sheriff. Actually, the three days I spent in a psych ward did not help me. It took me another year to quit. When I was ready, everything worked well because I had a good attitude (and it was also low cost).